Thanks for your suggestions, pholy.
You are right about the long lines, that must be why I get this (331) error.
I edited out 2 sections of "<p>" that seemed a bit weird , and it did the trick, my epub was delivered to Ibookstore !
I think what was causing a problem may have been either
<p class="calibre10 sgc-1"> </p>
right before the </body> tag
or
<p><span class="calibre7"><br class="calibre8" id="calibre_pb_7" /></span></p>
which was at the beginning.
Cheers